1. Field of the Invention
The invention relates to a portable terminal device with built-in GPS (global positioning system) and more particularly to a portable terminal device with built-in GPS of such a type that, when a plurality of persons each carry a portable terminal device with built-in GPS, a first portable terminal device with built-in GPS can set, for example, the designated movement range of a second portable terminal device with built-in GPS and, for the setting contents, the second portable terminal device with built-in GPS can automatically answer the first portable terminal device with built-in GPS.
2. Prior Art
For example, in a portable telephone (a cellular phone), when the power supply is in ON, the portable telephone notifies the base station side of its own position information, i.e., information on the service area in which the portable telephone is located, at predetermined timing. The use of the position information enables a portable telephone network system to grasp information on which portable telephone is located whereabouts on the topography.
In portable telephones, however, the position can be identified only for each cell covered by each base station. Therefore, the obtained position information is merely such that a portable telephone is present within a distance range of several km. There is a system utilizing GPS as a system which can identify the position of the portable telephone with higher accuracy. GPS is a positioning system utilizing military satellites of U.S.A. In this system, 24 GPS satellites each loaded with a precision atomic clock revolve six orbits, wherein four GPS satellites are assigned to each orbit. In GPS, a low-accuracy position information system called “C/A (clear/acquisition) code” has been opened for private purposes. A typical example of a system using C/A code is a car navigation system for automobiles (commonly known as “CARNAVI”). It is known that the use of the C/A code causes a position detection error of several tens of meters to about 100 m. DGPS (differential global positioning system) uses the C/A code and can improve the position accuracy to within about several meters. This DGPS has already been put to practical use.
GPS using the C/A code utilizes four GPS satellites disposed on one orbit and determines a difference, among the three GPS satellites out of the four GPS satellites, in time necessary for radio waves generated from the GPS satellite to reach a receiving point. Based on the time difference, the position is computed using a receiver at the receiving point. In this case, when there is an error between the clocks loaded on the GPS satellites and the clock loaded on the receiver, an error in distance between the three GPS satellites and the receiver occurs. In order to solve this problem, a distance from the fourth GPS satellite is taken into consideration to correct the time error and to provide accurate time. Thus, the positioning system using GPS requires the receipt of data from the four GPS satellites, for computing four variables, latitude, longitude, altitude, and time. The position of the receiving point is indicated in terms of three numerical values representing the latitude, longitude, and altitude, or indicated on a map in the display of the receiver. Specific examples of this system are described, for example, in Japanese Patent Laid-Open Nos. 289118/1994, 122895/1998, and 241925/1999.
In the system disclosed in Japanese Patent Laid-Open No. 289118/1994, each navigation terminal device has a GPS receiving section. A first navigation terminal device in the navigation terminal devices receives a coordinate position of a second navigation terminal device through a portable telephone network and simultaneously indicates, on an identical screen, its own coordinate position and the coordinate position of the second GPS terminal device. According to this construction, the positional relationship between coordinate positions of the plurality of navigation terminal devices can be visually grasped. This can be utilized in positioning of each person when several persons or a group of persons move together, or in the prevention of missing of children.
In the system described in Japanese Patent Laid-Open No. 122895/1998, a searching device has a communication function of PHS system and a positioning function of GPS. The searching device comprises a combination of a master telephone set and a slave telephone set. The position of the master telephone set and the position of the slave telephone set are indicated on a display of the master telephone set. The master telephone set and the slave telephone set together establish DGPS to improve the positional accuracy. According to this construction, even when a poriomania person or a victim, who carries the slave telephone set, is away from a searcher who carries the master telephone set, the position of the slave telephone set can be accurately located even though the person is in the crowd.
The system disclosed in Japanese Patent Laid-Open No. 241925/1999 comprises a management device, which is carried by a tour conductor or the like and a portable navigation device which is carried by tourists or the like. Information on places unsuitable for sightseeing, expected dangerous places, etc. is previously stored in the management device. The portable navigation device periodically acquires position information by GPS and sends this position information to the management device. As soon as the management device has judged that the current position of the portable navigation device is within or is close to the prescribed place or area stored in the management device, the management device sends, to the portable navigation device, an inhibit signal for stoppage of the entry into or approach to that area. This can prevent the person, who carries the portable navigation device, from being exposed to danger.
The conventional portable terminal devices with built-in GPS, however, have the following problems.
(1) According to the constructions of Japanese Patent Laid-Open Nos. 289118/1994 and 122895/1998, when the searcher (a person who carries a navigation terminal device and wishes to obtain position information from another navigation terminal device, or a person who carries a searching device as the master telephone set) does not have intention of conducting the search, any search is not carried out. Therefore, when a person to be located (a person who carries the another navigation terminal device, or a person who carries the slave telephone set) is in face of an unexpected accident which is a state of emergency, in some cases, the searcher cannot rapidly cope with the state of emergency.
(2) According to the constructions of Japanese Patent Laid-Open Nos. 289118/1994 and 122895/1998, the searcher cannot set the movement range of the person to be located. Therefore, the person to be located can be freely moved without limitation on the movement range, and, when the person to be located is a, person suffering from poriomania, such as old person, or a, child, the position of the person to be located should be always monitored. According to the construction of Japanese Patent Laid-Open No. 241925/1999, when the person to be located has approached or entered a preset place, alarm can be given to the person to be located who is then placed under restraint. The person to be located, however, can be freely moved to places other than the preset place. According to the construction of Japanese Patent Laid-Open No. 241925/1999, alarm can be given to a person who carries the portable navigation device. Since, however, the communication system is not a public portable telephone network but a private radio system, the person who carries the management device cannot make contact with the person to be located through a telephone. The system is private and thus is not general-purpose one.
(3) In all the above-described conventional techniques, the searcher side cannot be informed of the occurrence of an abnormal state or a change in state of the person to be located, based on the speed of movement of the person to be located. Therefore, upon the occurrence of such a state that, for example, a person is kidnapped and taken away in a car, the searcher cannot grasp this state. If the change in movement speed can be grasped, upon a rapid change in movement speed from the speed of walking to the speed of vehicle, the searcher can recognize the occurrence of an abnormal state based on this change.